Each service in the Event or Regular Inn got its own supervisor that provides additional bonuses to the particular service. For example Gordon Beef can be put only for restaurants, Strange Doc for Bars etc.

Supervisor can only be assigned to one Inn at a time (e.g. if a Supervisor is assigned to service in Inn #1, he can’t be assigned to the current Event Inn, and he is shown as BUSY in UI).
When Event is over, Supervisor automatically unassigned from the event inn and is not marked as BUSY in UI.

Play more events to get more supervisors :)